New Silicon-Coated Nanonets Show Promise as High-Capacity, Long-Life Li-ion Anode Material; Design Approach Viable for Other Materials
|Left. Schematic of the Si/TiSi2 heteronanostructure. Right. Charge capacity and Coulombic efficiency of the heteronanostructure with 8,400 mA/g charge/discharge rate tested between 0.150 and 3.00 V. Credit: ACS, Zhou et al. Click to enlarge.|
Researchers at Boston College have synthesized a unique heteronanostructure consisting of two-dimensional TiSi2 nanonets and particulate Si coating. Tested as the anode material for Li ion storage, at a charge/discharge rate of 8,400 mA/g, the researchers measured specific capacities of more than 1,000 mAh/g.
Only an average of 0.1% capacity fade per cycle was observed between the 20th and the 100th cycles. The combined high capacity, long capacity life, and fast charge/discharge rate represent one of the best anode materials that have been reported, according to the team.
A paper on their work was published online 11 February in the ACS journal Nano Letters.
Crystalline silicon (C-Si), with a theoretical specific capacity limit of 4,200 mAh/g, has attracted a large amount of research attention as a promising anode material for Li-ion batteries. However, the well-known problem of unmanageable volumetric expansion of silicon upon lithium ion insertion results in drastic and rapid capacity fading due to structural and electronic degradation.
A number of approaches have tackled this issue. A viable solution offering long capacity life and fast charge/discharge rate will require the ability to accommodate the volumetric change while maintaining superior charge transport.
The material proposed by Zhou et al. addresses both of those issues, they say. The strong performance was enabled by the capability to preserve the crystalline TiSi2 core during the charge/discharge process; the high conductivity and the structural integrity of the TiSi2 nanonet core enable reproducible Li+ insertion and extraction into and from the Si coating.
The performance achieved demonstrates the potential of this novel heteronanostructure design for other chemistries as well, they noted.
We have synthesized a novel Si/TiSi2 heteronanostructure as the anode material for Li+ batteries. In this structure, Si acts as an active component to store and release Li+ while TiSi2 serves as the inactive component to support Si and to facilitate charge transport. The differences between their electrochemical potentials in reacting with Li+ permit the selection of the operation potentials to keep TiSi2 intact. At a fast charge/discharge rate of 8400 mA/g, superior capacity retention of >99% per cycle at the level of 1,000 mAh/g over 100 cycles were obtained. Although bulk TiSi2 and other silicides have been studied as anode materials for Li ion batteries, this is the first report of using nanostructured TiSi2 for similar applications.
The essence of our design lies in the combination of a complex conductive core that does not participate in the lithiation process and a reactive coating that acts as the Li+ insertion and extraction medium. It shall be possible to extend the design other extensively studied materials as well, such as Ge, Sn, SnO2 and transition metal oxides.
—Zhou et al.
Sa Zhou, Xiaohua Liu and Dunwei Wang (2010) Si/TiSi2 Heteronanostructures as High-Capacity Anode Material for Li Ion Batteries. Nano Lett., Article ASAP doi: 10.1021/nl903345f